Question: Solve for $r$ : $-12 + r = -23$
Answer: Add $12$ to both sides: $ \begin{eqnarray} \\ -12 + r &=& -23 \\ \\ {+12} && {+12} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{-12 + r} &\hphantom{=}& \hphantom{-23} \\ r &=& -23 {+ 12} \\ \end{eqnarray} $ Simplify. $ r = -11$